Societal demands for greater automotive fuel economy, lower environmental impact, and enhanced vehicle performance have resulted in significant, industry-wide efforts to improve vehicle and fleet fuel economies. One area in which significant further gains in vehicle and fleet fuel economies can be realized is vehicle lightweighting. A number of vehicle lightweighting options have been devised and implemented. The vast majority of these options are based on material substitutions. In particular, there is a substantial and growing trend toward the use of aluminum alloys to replace ferrous metals in a variety of automotive components. While material substitutions of aluminum in place of steel have yielded significant reductions in vehicle mass, they have failed to fully exploit the potential of aluminum for vehicle weight reduction. This potential can be far more fully realized by the use of aluminum for the primary structure of the vehicle.
Presently, in the automotive industry, the primary method employed for vehicle body construction is the traditional sheet metal monocoque (or "unibody") structure. It is in virtually universal use in the automotive industry today. However, other design and construction approaches exist. One such alternative is the frame-on-body approach that is exemplified by the CHRYSLER PLYMOUTH PROWLER. Here, the vehicle body is mounted onto a separate structural frame that supports the engine, power train, and suspension components. In this type of design, the structural role of the body is much less than in the unibody class of designs.
On the design/construction spectrum at one end of which is the unibody approach there is at the other end, the multi-product aluminum space frame approach. In a space frame, the structure of the body consists of a number of extruded beams, joined together at nodes made from a variety of aluminum product forms. A multi-product aluminum space frame structure is shown in U.S. Pat. No. 4,618,163, entitled "Automotive Chassis", the contents of which are incorporated by reference as if fully set forth herein The structural truss which results from a space frame structure is then covered with a largely non-structural sheet-product skin to create the finished vehicle body.
The space frame approach yields a number of benefits to manufacturers, consumers, and society at large. These benefits include the reduced weight of the vehicle, the environmental benefits obtained through reduced fuel consumption and lower vehicle emissions, and the proven and commercially viable recyclability of aluminum parts.
The aluminum space frame vehicle structure is more versatile than the steel unibody counterpart. For example, a single frame design can be produced, with little or no modification, and function as a passenger car, a minivan, a sport utility vehicle, or light truck. The space frame structure permits the separation of the frame structure from the styling and passenger or load bearing configuration of the vehicle. This is possible because the external appearance of the vehicle can be altered without altering the internal structural frame.
It is the current practice to construct aluminum space frame vehicle structures of extruded members which are joined by welding to separately manufactured nodes. This assembly process requires fit-up and joining of a number of different product forms, e.g., castings, extrusions, stamped sheet, etc., of complex shape and often widely desperate sizes. Because the aluminum components are far more stiff than the sheet steel parts used for traditional unibody vehicles, they require "fit-up" forces far greater than those needed for sheet metal parts. The force levels required during assembly commonly exceed the capabilities of conventional automotive assembly fixtures. So, the geometric tolerances of the aluminum parts must be controlled much more closely than those of conventional sheet steel parts. Such tolerances are not always entirely compatible with existing part manufacturing processes, and aluminum parts may require machining and forming prior to assembly. The high structural stiffness of the components being joined, moreover, leads to difficult tolerance stack-ups at the joints, so that joint gaps and locations may vary somewhat from one assembly to the next.
It is therefore an object of the instant invention to promote the widespread use of the aluminum space frame vehicle structure concept, and elements thereof, through the use of innovative aluminum frame vehicle structure designs.
It is another object of this invention to mitigate or eliminate the manufactureability issues associated with current aluminum frame vehicle structures.
It is yet another object of this invention to eliminate the separate node components which characterize the current generation aluminum space frame vehicle structures and in their place utilize an integral node made of nested extrusions and/or pocketed joints.
It is here again another objective of this invention to address joint location and gap control in a space frame style body-in-white structure and to provide a design structure that provides a built-in allowance for the tolerance stack-up interferences that inevitably develops at the joints.
It is still a further object of this invention to facilitate and enable the high speed, mass production of aluminum frame vehicle structures.